Plasma is a highly ionized gas including positive ions and electrons. Plasma discharge is used for gas excitation to generate an active gas including ions, free radicals, atoms and molecules. An active gas is widely used in various fields. An active gas is generally used in semiconductor fabrication processes, for example, such as etching, deposition, cleaning, ashing and the like.
Types of plasma sources for generating plasma are diverse. Typical examples of plasma sources include capacitively coupled plasma using radio frequency and inductively coupled plasma. A capacitively coupled plasma source has an advantage in that processing productivity is high compared with the other plasma sources because the capability of accurately controlling capacitive coupling and ions is excellent. However, when electrodes for capacitive coupling become bigger to process a large substrate to be processed, the electrodes are likely to be fired, to be deformed or damaged. In this case, since the intensity of an electric field becomes disuniform, the density of plasma is disuniform and the inside of a reactor is likely to be contaminated. Similarly, when the area of an inductive coil antenna is big, an inductively coupled plasma source is difficult in generating plasma in uniform density.
In the semiconductor fabrication industry, more improved plasma processing technologies are required as semiconductor devices are super-miniaturized, silicon wafer substrates to fabricate semiconductor circuits become large, glass substrates to manufacture liquid crystal displays become large and new materials to be processed are developed. Specifically, plasma sources and plasma processing technologies are needed to be improved to be capable of excellently processing large-area substrates.
As the substrates to be processed become large, the entire equipment for production also becomes large and thus the entire area for the equipment increases. Consequently, these result in an increase in the cost of production. In this regard, a plasma reactor and a plasma processing system are needed to minimize the area for the equipment if possible. Specifically, in the semiconductor fabrication process, the productivity per unit area is one of the important factors influencing on the price of a final product. To increase the productivity per unit area, there have been proposed the techniques of effectively laying out the constitution of the production equipment. For example, a plasma rector has been provided to process two substrates in parallel. However, since most plasma reactors to process two substrates have two plasma sources, these substantially fail to minimize the processing equipment.
However, if two or more plasma reactors are positioned in parallel vertically or horizontally so as to share the common parts of each constitution and to parallel process two substrates by using a single plasma source, many advantages can be produced by the reduction of the equipment space and the minimize of the equipment constitution.
Many efforts to increase productivity are continuously made in the semiconductor industry, like the other industries. To increase the productivity, the production equipment needs to be basically increased or improved. However, when the production equipment merely increases, the cost of increasing the processing equipment is incurred and the space equipment for a cleaning room needs to be increased, resulting in high cost.